The present invention relates to devices for recording information on sheet material, and more particularly to sheet advance platens having alignment pins which are retractable during some portion of the rotation of the platen.
Cylindrical printing platens are widely used in such applications as computer print-out devices, teletype machines, typewriter, etc. It has been recognized that positive advance and accurate alignment of the sheet material can be realized by providing these platens with circumferentially disposed sheet alignment pins. These alignment pins can be particularly useful in applications requiring close registry of multiple sheets, or where pre-printed sheet forms must be precisely positioned during the printing operation.
Since these pins extend beyond the outer surface of the platen, they tend to interfere with the operation of the printing head for at least a portion of its motion across the platen. This results in a corresponding limitation in the width of paper upon which information may be recorded. More efficient use may be made of the full width of the paper if the pins are deleted, however the advantages inherent in the use of alignment pins is then lost.
It is therefore an object of the present invention to provide information recording apparatus which includes a platen having alignment pins and which yet retains the advantages of platens not having such pins.
It is another object of the present invention to provide a printing platen for use with the printing station and which has alignment pins circumferentially disposed thereon which are retracted during travel past the recording station so as to prevent interference therewith.
It is yet another object of the present invention to provide printing apparatus which provides positive advance of the sheet material and also allows use of a relatively wide printing field.
In accordance with the present invention, recording apparatus is provided including a platen having a plurality of alignment pins disposed thereon for engaging corresponding perforations in the sheet material to be printed upon. A recording station is disposed adjacent the platen for imparting information to the sheet material. Means are included for rotating the platen so as to feed the material past the recording station. Further means are provided for retracting each of the pins during that portion of the rotation of the platen when that pin is passing the recording station.